Increase default decimal precision

[glowacki-dev]

Default harcoded decimal precision of 6 becomes problematic when tracking cryptocurrency transactions. Lots of them are divisible with a higher precision which causes small rounding errors when tracking values and holdings.
Most of the time it would be negligible (it would be sub-cent difference) but a difference of 0.000001 BTC is roughly $0.1 which can add up to significant numbers with multiple transactions.

Changes made:

• Increase default precision from 6 to 8 (enough to accurately track BTC holdings)
• Replaced hardcoded precision in UI components with constants, which would make it easier to change when needed and keep in sync with backend
• Updated asset lots table to properly format asset quantity

This PR isn't a real fix for the underlying issue - to do this the precision should probably be user-configurable or automatically determined based on tracked assets. It makes the issue less annoying though and lays some groundwork for allowing proper configuration for this value

[afadil]

is it possible to update this PR?
Thanks

[afadil]

done in v3.0.4